Research Article: Loss of bronchoprotection to Salbutamol during sputum induction with hypertonic saline: implications for asthma therapy

Date Published: May 10, 2018

Publisher: BioMed Central

Author(s): Hongyu Wang, Melanie Kjarsgaard, Terence Ho, John D. Brannan, Parameswaran Nair.


Sputum induction with hypertonic saline in obstructive airway diseases is generally safe. However, saline induces bronchoconstriction in some patients despite pre-medication with Salbutamol. Our objectives were to investigate the predictors of failure of Salbutamol to protect against saline-induced-bronchoconstriction in patients with asthma and COPD and to evaluate implications for asthma therapy.

Retrospective survey on a database of 3565 patients with obstructive airway diseases who had sputum induced with hypertonic saline. The effect of baseline FEV1, bronchitis and concomitant medication on saline-induced-bronchoconstriction (≥ 15% drop in FEV1) were examined by logistic regression analysis. A subgroup had this re-examined 8–12 weeks after decreasing long-acting-beta-2-agonist dose or after adding Montelukast, which included an assessment of mast cell activity in sputum.

222 (6.2%) patients had saline-induced-bronchoconstriction despite pre-treatment with inhaled Salbutamol. Baseline airflow obstruction (FEV1% predicted < 60% OR 3.29, p < 0.001) and long-acting-beta-agonist use (OR 2.02, p = 0.001), but not bronchitis, were predictors of saline-induced-bronchoconstriction, which decreased when long-acting-beta-agonist dose was decreased. Refractoriness to subsequent bronchodilation was associated with mast cell activity and was attenuated by Montelukast. Sputum induction with saline provides information on bronchitis and additional physiological data on tolerance to beta-agonists and mast cell activity that may have implications for clinical therapy.

Partial Text

Hypertonic saline nebulization is a relatively non-invasive procedure to collect sputum for airway diseases even in the presence of moderate to severe airflow obstruction [1]. Occasionally, despite pre-medication with Salbutamol, saline-induced bronchoconstriction (SIB) occurs. This may be related to baseline airflow obstruction, increased airway hyperresponsiveness (AHR), or lowered sensitivity to β2-agonists [2–5]. The loss of bronchoprotection is considered to be primarily due to β2-receptor downregulation and desensitization [3], and the refractoriness to subsequent bronchodilation with Salbutamol (i.e. recovery time) is considered to be mediated partly by leukotrienes and thus reflecting mast cell activity [6].

Data were collected from a computerized database of induced sputum cell counts from January, 2004 to January, 2008 at the Firestone Institute for Respiratory Health in Hamilton, Ontario. The database contained the following information: age, gender, post-bronchodilator spirometry, FEV1 after each concentration increment of saline (3, 4, 5%, each for 7 min), and after subsequent administration of Salbutamol, sputum cell counts, referring physician diagnosis, indication for the test, and current relevant medications. Three groups of patients were included in the analysis: current asthma with or without associated chronic airflow limitation, possible asthma (when the referring physician was not certain of the diagnosis), and non-asthmatic COPD. A diagnosis of asthma was based on previous evidence of reversible airflow limitation (an increase in FEV1 ≥ 15% and ≥ 200 ml from the pre-bronchodilator value) or airway hyper responsiveness (a provocative concentration of methacholine causing a > 20% fall in FEV1 < 8 mg/ml). COPD was indicated by a post-bronchodilator FEV1/VC < 70%, and history of cigarette smoking or smoker’s inclusions within macrophages. 3565 patients had sputum induced for the assessment of bronchitis (Table 1), of whom 222 (6.2%) had a ≥ 15% fall in FEV1. Overall, the predictors of Salbutamol failing to protect against SIB were the use of LABA (OR 2.02, 95% CI 1.32–3.01, p = 0.001), high doses of ICS (OR 1.85, 95% CI 1.11–3.09, p = 0.02), and baseline airflow obstruction (FEV1/VC < 70%; OR 2.08, 95% CI 1.40–3.10, p < 0.001) and FEV1 predicted < 60% (OR 3.29, 95% CI 2.06–5.26, p < 0.001). The presence or type of bronchitis were not predictors (Table 2). In the subset of patients who had a concurrent methacholine test (n = 56), a PC20 methacholine of < 2 mg/ml was significantly associated with SIB (OR 7.50, 95% CI 2.04–22.66, with p = 0.002 by Fisher’s exact test).Table 1Baseline characteristics of patientsPatients, no. (%)All patientsn = 3565Asthman = 2013Possible asthman = 157Non-asthmatic COPDn = 1395FEV1 ↓ > 15% (%)222 (6.2)152 (7.5)22 (14.0)48 (3.4)Male sex (n, %)1569 (44.0)708 (40.3)100 (63.7)761 (54.5)Age year (mean, SD)54 (17)47 (17)44 (13)66 (11)ICS (n, %)1957 (54.9)1661 (82.5)102 (65)194 (13.9)LABA (n, %)2426 (68)1381 (68.6)51 (32.5)994 (71.3)OCS (n, %)174 (4.9)135 (6.7)8 (5.1)31 (2.2)NB (n, %)328 (16.6)106 (5.3)15 (9.6)207 (14.8)EB (n, %)592 (13.8)534 (26.5)20 (12.7)37 (2.7)FEV1 % (mean, SD)62.5 (45.5)68.7 (33.6)78.4 (22.5)59.8 (40.8)FEV1/VC % (mean, SD)64.4 (37.0)68.7 (43.7)72.2 (24.6)54.6 (34.5)ICS inhaled corticosteroid, NB neutrophilic bronchitis, EB eosinophilic bronchitis, OCS oral corticosteroid, regular or intermittent, LABA long-acting β-agonistEosinophilic bronchitis (EB) was defined as percentage of sputum eosinophils ≥ 3%. Neutrophilic bronchitis (NB) was defined as a total cell count ≥ 15 million cells/g of sputum and proportion of neutrophils ≥ 64%Table 2Predictors of saline-induced bronchoconstrictionAll patients, n = 3565No.FEV1 fall > 15%, no. (%)OR (95% CI)p valueHigh ICS dose78584 (10.7)1.85 (1.11–3.09)0.019LABA use2426142 (10.0)2.02 (1.32–3.10)0.001FEV1 < 60% predicted59693 (15.6)3.29 (2.06–5.26)< 0.001FEV1/VC < 70%1165149 (12.8)2.08 (1.40–3.10)< 0.001ICS inhaled corticosteroid, LABA long-acting β-agonist We confirmed previous observations that baseline airflow limitation and airway hyperresponsiveness to a direct stimulus such as methacholine can predict the loss of bronchoprotection to Salbutamol during saline induction [2], but also established that LABA use is a risk factor in a mixed population of obstructive airway diseases. LABA appears to cause these effects by way of receptor tolerance, [10–13]. β-receptor tolerance of airway smooth muscle cells can manifest as reduced bronchodilation, whereas for mast cells may manifest with an increased propensity to release inflammatory mediators [14]. For those on high-dose LABA, we found that reducing the dose by half led to the resolution of SIB in almost 70% of subjects. This suggests that it is important to recognize this phenomenon and to reduce the dose of LABA rather than increasing it in those patients with asthma who may have tolerance either to its bronchodilator or bronchoprotective effects. In summary, we report two clinically relevant findings regarding airway pathophysiology that could be gleaned during the process of sputum induction using hypertonic saline: first, failure of Salbutamol to protect against saline-induced bronchoconstriction should raise suspicion of tolerance to the bronchoprotective effect of β-agonists. Such patients may benefit from reducing the dose or frequency of use of LABA. Second, a prolonged recovery time (refractoriness) of FEV1 following saline bronchoconstriction may indicate mast cell activity and may suggest that these are patients who may respond to mast-cell directed therapy or therapy directed against products of mast cells such as leukotriene receptor antagonists. It would be relevant to examine this phenomenon in relation to the mast cell signatures that have recently been reported using transcriptomic analysis of sputum [15, 16]. It is important to test both LABA dose reduction to improve β-agonist sensitivity and mast-cell targeted therapy to improve refractoriness to hyperosmolar stimuli induced bronchoconstriction in placebo-controlled randomised clinical trials.   Source:


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